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How to better focus waves by considering symmetry and information loss

Author(s)
Lou, KaiGranick, SteveAmblard, Francois
Issued Date
2018-06
DOI
10.1073/pnas.1803652115
URI
https://scholarworks.unist.ac.kr/handle/201301/24406
Fulltext
http://www.pnas.org/content/115/26/6554
Citation
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, v.115, no.26, pp.6554 - 6559
Abstract
We amend the general belief that waves with extended spherical wavefront focus at their center of curvature. Instead, when the spherical symmetry of waves is broken by propagating them through a finite aperture along an average direction, the forward/backward symmetry is broken and the focal volume shifts its center backward along that direction. The extent of this focal shift increases as smaller apertures are used, up to the point that the nominal focal plane is out of focus. Furthermore, the loss of axial symmetry with noncircular apertures causes distinct focal shifts in distinct axial planes, and the resulting astigmatism possibly degrades the axial focusing resolution. Using experiments and simulations, focal shift with noncircular apertures is described for classical and temporal focusing. The usefulness of these conclusions to improve imaging resolution is demonstrated in a highr-esolution optical microscopy application, namely line-temporal focusing microscopy. These conclusions follow from fundamental symmetries of the wave geometry and matter for an increasing number of emerging optical techniques. This work offers a general framework and strategy to understand and improve virtually any wave-based application whose efficacy depends on optimal focusing and may be helpful when information is transmitted by waves in applications from electromagnetic communications, to biological and astronomical imaging, to lithography and even warfare.
Publisher
NATL ACAD SCIENCES
ISSN
0027-8424
Keyword (Author)
diffraction theoryfocal shiftimagingtwo-photon microscopyspatiotemporal focusing
Keyword
CONVERGING SPHERICAL WAVESBOUNDARY DIFFRACTION WAVEMAGGI-RUBINOWICZ THEORYFOCAL-SHIFTGAUSSIAN BEAMSELECTROMAGNETIC DIFFRACTIONINTEGRAL-REPRESENTATIONOPTICAL SYSTEMSFRESNEL-NUMBERCOHERENT BEAM

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